Research for new pyrethroids is motivated by the fact that pyrethrum [a mixture of esters of crysanthemic acid (2,2-dimethyl-3-isobutenyl-cyclopropanecarboxylic acid) with a retronolone (2-alkenyl-3-methyl-cyclopent-2-en-4-olone)] is an insecticide of a natural origin, having a high insecticidal activity. For example, pyrethrum provides fast and strong insecticidal action by contact on winged insects, and with a low toxicity on mammals by oral administration, combined with a negligible dermal toxicity. However, the particular structure of the molecule renders pyrethrum easily degradable under atmospheric agents and, thus, it has no persistent action, a characteristic that does not allow its use in the protection of agricultural cultivations, limiting its use solely to domestic environments.
Research was thus oriented towards the synthesis of new compounds that, recalling the structure of pyrethrum, maintain its positive characteristics such as the high insecticidal activity and the low toxicity for mammals, while at the same time they are more resistant to the action of atmospheric agents.
There have been prepared numerous synthetic pyrethroids some of which displayed interesting characteristics [see for instance "Synthetic Pyrethroids" (by M. Elliot Ed.), ACS Symposium Series No. 42, Washington 1977].
Recently, in German Patent Application DOS No. 2730515 (Bayer), Phenoxy-benzyl cyclopropanecarboxylic esters substituted in position 3 of the cyclopropane ring by a vinyl group in its turn substituted by a halogen atom and by an optionally substituted phenyl-thio group, have been described.